by
ABSTRACT
The optimal dietary protein requirement of seabass, Lates calcarifer Bloch in early grow-out phase (71–182 g) was determined over a four-month (125 days) period using protein reference diets of crude protein (CP) 40, 45 and 50 percent, derived from a single protein source, fish meal. Dietary lipid (ether extractable fat) was fixed at 12 percent. The study was carried out under controlled tank conditions, in triplicate, with trash fish as control feed.
The optimal dietary protein requirement of seabass was 40–45 percent. This was determined by assessing fish growth rate, feed conversion ratio, protein efficiency ratio and apparent protein retention (protein conversion efficiency). Although fish growth rate was significantly higher with trash fish feed, feed conversion ratio (FCR) was not significantly different among treatments. Poorer protein utilization for growth in trash fish fed seabass was reflected in apparent protein retention figures which were significantly lower. This is possibly related to digestible energy sources of the feed.
A second experiment was conducted to assess the performance of two practical dry formulations made up from multiple protein sources on seabass from the same population. The cheaper local formulation containing CP 43 percent and 12 percent ether extractable fat performed better than imported seabass feed of higher CP 50 percent and ether extractable fat 16 percent. Protein efficiency ratio of 1.66:1 with the local formulation was significantly higher than PERs with the imported seabass feed and trash fish.
Protein quality of the formulated test diets was comparable, but was better in trash fish. Calculated digestible energy (DE) values for all diets were 3 297–4 160 kcal/kg or 131–218 mg/kcal of dry feed. In trash fish feed, 87.2 percent of total DE was derived from protein and the rest (12.8 percent) from fat. In the test diets, 52.3–57.4 percent of total DE was derived from protein, 31.8–38.1 percent from fat and 9.6–12.1 percent from carbohydrate. Protein sparing was, therefore, more effective with the test diets than with trash fish where the main energy source of the fish was likely to have been the protein. This could explain the significantly lower protein retention in seabass fed trash fish.
1. INTRODUCTION
The seabass, (Lates calcarifer Bloch) is the most popularly farmed food fish in coastal waters of Singapore. Little work has been done in defining the nutritional requirements of the seabass under culture conditions. Such knowledge would be vital in the formulation of a balanced and costeffective diet. Information of dietary protein requirement is important when considering a formulated diet because protein sources usually make up its most expensive component. Dietary protein could also be utilized for energy unless spared by a cheaper energy source like fat. The utilization of protein for energy would result in a drop in protein conversion efficiency (Adron, et.al., 1976).
1 Primary Production Officer,
2 Senior Primary Production Officer, Marine Aquaculture Section, Primary
Production Department, 8th Storey, Maxwell Road, Singapore 0106
Quantitative requirement of dietary protein of fish in this experiment was determined by using protein reference diets and by analysis of the feed ingredients. By feeding the fish with known levels of protein, the optimum level of dietary protein required by the fish can be evaluated. The optimum level of dietary protein which results in maximum growth has been studied in many species under culture conditions. Optimum protein levels between 40–55 percent and 47–50 percent result in highest growth for chinook salmon (Oncorhynchus tschawytscha) and European seabass (Dicentrarchus labrax) (DeLong, et. al., 1958; Metailler and Mery, 1977 and Alliot, et. al., 1974). It was found that the optimum dietary protein level for flatfish (Pleuronectes platessa) is 52 percent (Cowey, et. al., 1972). In other marine carnivorous species such as estuary grouper (Epinephelus salmoides) and red sea bream (Chrysophrys major), optimum dietary protein requirement is at levels 40–50 percent and 55 percent, respectively, (Teng, et. al., 1978 and Yone, 1976). The dietary protein requirement of locally cultured spotted grouper (Epinephelus tauvina) is around 45 percent (PPD, unpublished).
2. MATERIALS AND METHODS
2.1 The tank system
A series of 18 fiberglass tanks (80 × 50 × 60 cm height), 240-liter capacity; seawater volume of 160 l/tank was used in the experiment. The tanks were continuously supplied with filtered seawater at a rate of 2.6 liters per minute per tank (one change per hour). Seawater (salinity 30 ± 2 percent) was pumped from two 2.5 m3 header tanks via two high pressure sand filters (diameter 26 cm) by alternating two self-priming centrifugal seawater pumps of 1.5 HP each delivering filtered seawater to the tank system. The water temperature was 28 ± 2°C.
2.2 The fish
Seabass used in this experiment were imported as fingerlings from Thailand such as are usually purchased by commercial fish farms for growing out to market size in netcages. The fish were weaned from trash fish to dry pelleted feed over a period of two weeks. The weaned seabass [Total Length (TL) 14 cm; Body Weight (BW) 71 g] were selected at TL and BW not exceeding 10 percent CV (Coefficient of Variation) and randomly distributed in the experimental tanks at seven fishes per tank.
2.3 Carcass composition
Three random fish samples per treatment were sacrificed at the start and end of the experiment and finely ground for whole carcass composition. Carcass moisture, crude protein, ether extractable fat and total ash were analyzed.
2.4 The experimental diets
The study was conducted with two feed groups. The first group of diets was designed to determine the optimal dietary protein requirement of seabass, and were prepared at protein levels of 40, 45 and 50 percent with lipid (ether extractable fat) of 12 percent. The diets were designated A, B and C, respectively. Seabass in control tanks were fed trash fish (Diet F). The protein source of each diet was fish meal.
The next series of diets, designated D and E were practical diet formulations made up from several protein sources and aimed at comparing fish growth rates with that of trash fish control. Practical formulations are preferred to reduce over-reliance on a single protein source. Diet D was a practical local formulation devised by the Primary Production Department's Marine Aquaculture Section, while Diet E was a practical seabass formulation obtained from overseas. Diet E protein level was declared as 52 percent (actual analyzed level 50 percent) and 16 percent ether extractable fat (actual analyzed level 16 percent) on as-fed basis. If successful, such formulations are more readily transferable to the commercial sector than a protein reference diet.
All diets in this experiment were prepared by compression through a slow grinder and die of hole size 3 mm. The semi-moist pellets were dried on racks in a dehumidified, air-conditioned room (temperature 22–24°C) to moisture of between 7–10 percent. The feeds were stored in plastic bags at 22–24°C. The experiment was conducted using three replicate tanks of fish per test diet.
2.5 Proximate composition of experimental diets
Experimental diets were analyzed at the start of the experiment for moisture, crude protein, ether extractable fat, crude fiber, total ash, calcium and phosphorus at the Veterinary Research and Training Institute of the Primary Production Department. The proximate composition of test diets and calculated digestible energy values are shown in Table 1. Table 2 gives the amino acid composition of the diets.
2.6 Feeding
Feed was given by hand four times daily at 0900, 1030, 1200 and 1400 hours. Care was taken to ensure that the fish consumed until satiation and all that was offered. The amount of feed consumed daily was determined for each tank. Chopped trash fish was stored in air tight plastic boxes and frozen in between and after feeds.
2.7 Fish performance data collection
All fish were measured and weighed at four-week intervals during the 125-day experiment. Lengths (total and standard) and weights were recorded to the nearest 0.1 cm or 0.1 g. Quinaldine was used to anaesthetize the fish and excess water was removed with a soft cloth before weighing.
3. RESULTS
3.1 Optimal dietary protein requirement of seabass
This is evaluated in terms of fish growth rate, feed conversion ratio (FCR), protein efficiency ratio (PER) and apparent protein retention (protein conversion efficiency), and by a comparison of protein quality and digestible energy values and source.
Table 1. Proximate composition of experimental diets (percent)
| Diet | ||||||
|---|---|---|---|---|---|---|
| A | B | C | D | E | F | |
| As-fed basis | ||||||
Moisture | 6.8 | 7.1 | 7.5 | 10.0 | 7.7 | 77.3 |
Protein | 40.5 | 44.9 | 49.6 | 43.1 | 50.2 | 18.5 |
Ether extractable fat | 12.0 | 12.3 | 12.2 | 12.1 | 16.3 | 1.2 |
Ash | 19.1 | 18.3 | 30.1 | 13.2 | 8.3 | 4.9 |
-Ca | 4.2 | 4.5 | 1.9 | 2.5 | 1.4 | 1.1 |
-P | 2.6 | 3.0 | 2.1 | 2.2 | 1.3 | 0.2 |
Crude fiber | 4.5 | 0.7 | 0.7 | 1.1 | 0.3 | 0.1 |
| Dry basis | ||||||
Protein | 43.4 | 48.3 | 53.6 | 47.9 | 54.4 | 81.5 |
Ether extractable fat | 12.9 | 13.2 | 13.2 | 13.4 | 17.6 | 5.3 |
Ash | 20.5 | 19.7 | 32.5 | 14.7 | 9.0 | 21.6 |
-Ca | 4.5 | 4.8 | 2.1 | 2.8 | 1.5 | 4.8 |
-P | 2.8 | 3.2 | 2.3 | 2.4 | 1.4 | 0.9 |
Crude fiber | 4.8 | 0.8 | 0.8 | 1.2 | 0.3 | 0.4 |
Carbohydrate (calculated) | 10.0 | 10.0 | 10.0 | 10.0 | 10.0 | nil |
| Calculated energy | ||||||
Digestible energy* (kcal/kg dry diet) | 3 297 | 3 520 | 3 732 | 3 522 | 4 160 | 3 737 |
Digestible energy* (mg/kcal dry diet) | 132 | 137 | 144 | 136 | 131 | 218 |
Table 2. Amino acid composition of experimental diets (percent)
| Components (g/kg/dry diet) | Diet | |||||
|---|---|---|---|---|---|---|
| A | B | C | D | E | F | |
| Crude protein | 434 | 483 | 536 | 479 | 544 | 815 |
| Total amino acids | 402 | 468 | 474 | 441 | 499 | 800 |
| Essential amino acids | 173 | 187 | 234 | 187 | 193 | 431 |
| Arginine | 32 | 27 | 34 | 24 | 43 | 79 |
| Histidine | 10 | 8 | 16 | 18 | 10 | 41 |
| Leucine | 25 | 22 | 37 | 27 | 24 | 51 |
| Isoleucine | 10 | 10 | 17 | 12 | 12 | 28 |
| Lysine | 39 | 45 | 54 | 37 | 38 | 102 |
| Methionine | 13 | 18 | 13 | 16 | 14 | 22 |
| Phenylalanine | 19 | 18 | 22 | 16 | 20 | 27 |
| Threonine | 14 | 24 | 20 | 21 | 17 | 33 |
| Tryptophan | - | - | - | - | - | - |
| Valine | 11 | 15 | 21 | 16 | 15 | 48 |
| Non-essential amino acids | 228 | 282 | 240 | 252 | 305 | 370 |
| Tyrosine | 10 | 18 | 12 | 11 | 14 | 24 |
| Glycine | 29 | 39 | 30 | 32 | 37 | 48 |
| Alanine | 28 | 40 | 36 | 34 | 38 | 51 |
| Aspartic acid | 37 | 52 | 39 | 36 | 57 | 66 |
| Glutamic acid | 61 | 71 | 76 | 67 | 85 | 111 |
| Cystine | 3 | 2 | 1 | 1 | 1 | Neg |
| Proline | 40 | 30 | 23 | 49 | 41 | 37 |
| Serine | 20 | 30 | 23 | 22 | 32 | 33 |
3.1.1 Fish growth rate
Growth data is presented in Tables 3a and 4. There was a significant difference to 0.05 percent between fish fed all test diets and the control group fed trash fish. Highest normal growth rate of 1.08–1.25 g/ fish/day (mean 1.19 g/fish/day) was recorded in control fish. Among the test diets, highest growth rate of 0.76–1.04 g/fish/ day (mean 0.90 g/fish/day) was monitored in fish fed Diet B. The mean normal growth rate of fish fed Diet B is 75.6 percent of the mean growth rate of trash fish fed control.
The relative growth rate which is a more standardized measure was 0.84–0.91 percent per day (mean 0.86 percent per day) in fish fed trash fish and 0.71–0.81 percent per day (mean 0.77 percent per fish per day) for fish fed Diet B.
3.1.2 Feed conversion ratio (FCR)
There is no significant difference in the feed conversion ratio (dry basis) for all the protein reference diets A-C (Tables 3a and 4). Best results were obtained from fish fed Diets B and C being 1.08–1.20 (mean 1.14) and 1.02–1.17 (mean 1.10) to 1, respectively. Poorest results of 1.19–1.71 (mean 1.41) to 1 in this series were obtained with trash fish feed.
Table 3a. Feeding and growth data of seabass fed protein reference diets during the 125-day experiment
| Tank No. | Diet | Total fish days1 | Feed intake2(g) (× 7 fish × 125 days) | Cal. protein intake (× 7 fish × 125 days) dry basis | Percent range daily feed intake | Initial | Final | Total weight gain of 7 fish (g) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean standard length (cm) | Mean weight (g) | Total weight of 7 fish (g) | Condition3 factor | Mean standard length (cm) | Mean weight (g) | Total weight of 7 fish (g) | Condition3 factor | ||||||||
| as-fed | dry basis | ||||||||||||||
| 2 | A | 875 | 1 100.8 | 1 026.0 | 445.3 | 1.21 | 14.9±0.5 | 77.0±6.5 | 539.0 | 24.8 | 20.2±1.6 | 198.4±45.3 | 1 388.8 | 24.1 | 849.8 |
| 6 | A | 875 | 948.6 | 884.1 | 384.7 | 1.09 | 14.7±0.6 | 75.9±7.0 | 531.3 | 23.9 | 19.3±1.1 | 173.9±25.9 | 1 217.3 | 24.2 | 686.0 |
| 14 | A | 875 | 805.2 | 750.4 | 325.7 | 1.12 | 14.4±0.3 | 69.9±5.3 | 489.3 | 23.4 | 18.4±1.0 | 146.8±28.9 | 1 027.6 | 23.6 | 538.3 |
 | 875 | 951.5 | 886.8 | 385.2 | 1.14 | 14.7 | 74.3 | 519.9 | 24.0 | 19.3 | 173.0 | 1 211.2 | 24.0 | 691.4 | |
| 1 | B | 875 | 1 125.4 | 1 045.5 | 505.0 | 1.22 | 14.7±0.5 | 73.5±7.6 | 514.5 | 23.1 | 20.4±1.1 | 203.0±24.6 | 1 421.0 | 23.9 | 906.5 |
| 8 | B | 875 | 853.3 | 792.7 | 382.9 | 1.10 | 14.3±0.4 | 66.0±6.9 | 462.0 | 22.6 | 18.5±1.0 | 160.5±31.4 | 1 123.5 | 25.3 | 661.5 |
| 10 | B | 875 | 898.6 | 834.8 | 403.2 | 1.11 | 14.1±0.6 | 65.7±5.9 | 459.9 | 23.4 | 19.2±0.6 | 176.5±23.4 | 1 235.5 | 24.9 | 775.6 |
| 875 | 959.1 | 891.0 | 430.4 | 1.14 | 14.4 | 68.4 | 478.8 | 23.0 | 19.4 | 180.0 | 1 260.0 | 24.7 | 781.2 | |
| 5 | C | 875 | 816.4 | 755.2 | 404.8 | 1.20 | 14.1±0.5 | 66.0±6.1 | 462.0 | 23.5 | 18.7±0.9 | 162.2±15.8 | 1 135.4 | 24.8 | 673.4 |
| 9 | C | 875 | 916.7 | 848.0 | 454.5 | 1.09 | 14.8±0.4 | 75.1±8.1 | 525.7 | 23.2 | 20.1±1.2 | 193.5±34.2 | 1 354.5 | 23.8 | 828.8 |
| 11 | C | 875 | 917.3 | 848.5 | 454.8 | 1.14 | 14.2±0.4 | 69.2±6.4 | 484.4 | 24.2 | 19.2±1.2 | 172.6±31.7 | 1 208.2 | 24.4 | 723.8 |
| 875 | 883.5 | 817.2 | 438.0 | 1.14 | 14.4 | 70.1 | 490.7 | 23.6 | 19.3 | 176.1 | 1 232.7 | 24.3 | 742.0 | |
| 3 | F | 875 | 5 701.7 | 1 294.3 | 1 054.9 | 5.63 | 15.0±0.3 | 72.9±6.4 | 510.3 | 21.6 | 20.9±1.4 | 228.4±27.3 | 1 598.8 | 25.0 | 1 088.5 |
| 13 | F | 789 | 6 229.5 | 1 414.1 | 1 152.5 | 5.68 | 15.2±0.5 | 81.8±6.6 | 572.6 | 23.3 | 21.1±1.1 | 235.0±26.2 | 1 645.0 | 25.0 | 1 072.4 |
| 16 | F | 757 | 7 110.8 | 1 614.2 | 1 315.6 | 6.92 | 14.5±0.5 | 72.3±7.6 | 506.1 | 23.7 | 20.2±1.6 | 207.0±37.0 | 1 449.0 | 25.1 | 942.9 |
| 807 | 6 347.3 | 1 440.9 | 1 174.3 | 6.08 | 14.9 | 75.7 | 529.7 | 22.9 | 20.7 | 223.4 | 1 564.3 | 25.0 | 1 034.6 | |
1 Total fish days = ∑(No. fish each day)
2 
where n = 7 fish; d = 125 days
Table 3b. Feeding and growth data of seabass fed protein reference diets during the 125-day experiment
| Tank No. | Diet | Total fish days1 | Feed intake2(g) (× 7 fish × 125 days) | Cal. protein intake (× 7 fish × 125 days) dry basis | Percent range daily feed intake | Initial | Final | Total weight gain of 7 fish (g) | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean standard length (cm) | Mean weight (g) | Total weight of 7 fish (g) | Condition3 factor | Mean standard length (cm) | Mean weight (g) | Total weight of 7 fish (g) | Condition3 factor | ||||||||
| as-fed | dry basis | ||||||||||||||
| 4 | D | 875 | 985.2 | 886.7 | 424.7 | 1.23 | 14.4±0.5 | 698±5.3 | 488.6 | 23.4 | 18.7±1.0 | 164.7±27.3 | 1 152.9 | 25.2 | 664.3 |
| 15 | D | 875 | 970.6 | 873.6 | 418.5 | 1.15 | 14.4±0.8 | 72.0±7.2 | 504.0 | 24.1 | 19.3±1.2 | 170.8±26.2 | 1 195.6 | 23.8 | 691.6 |
| 18 | D | 875 | 965.6 | 869.0 | 416.3 | 1.14 | 14.9±0.5 | 77.2±7.9 | 540.4 | 23.3 | 197.7±1.4 | 182.1±37.0 | 1 274.7 | 23.8 | 734.3 |
| 875 | 973.8 | 876.4 | 419.8 | 1.17 | 14.6 | 73.1 | 511.0 | 23.6 | 19.2 | 172.5 | 1 207.7 | 24.3 | 696.7 | |
| 7 | E | 875 | 1 011.4 | 933.5 | 507.8 | 1.40 | 13.8±0.2 | 58.0±3.7 | 406.0 | 22.1 | 18.3±1.2 | 147.5±25.1 | 1 032.5 | 24.1 | 626.5 |
| 12 | E | 763 | 1 164.5 | 1 074.8 | 584.7 | 1.16 | 14.7±0.6 | 75.9±7.9 | 531.3 | 23.9 | 20.4±1.1 | 190.4±31.8 | 1 332.8 | 22.4 | 801.5 |
| 17 | E | 875 | 1 018.5 | 940.1 | 511.4 | 1.28 | 13.8±0.2 | 58.0±3.7 | 406.0 | 22.1 | 18.8±1.6 | 156.1±38.0 | 1 092.8 | 23.5 | 686.8 |
| 837.7 | 1 064.8 | 982.8 | 534.6 | 1.28 | 14.1 | 64.0 | 447.8 | 22.7 | 19.2 | 164.7 | 1 152.7 | 23.3 | 704.9 | |
| 3 | F | 875 | 5 701.7 | 1 291.3 | 1 054.9 | 5.63 | 15.0±0.3 | 72.9±6.4 | 510.3 | 21.6 | 20.9±1.4 | 228.4±42.3 | 1 598.8 | 25.0 | 1 088.5 |
| 13 | F | 789 | 6 229.5 | 1 414.1 | 1 152.5 | 5.68 | 15.2±0.5 | 81.8±6.6 | 572.6 | 23.3 | 21.1±1.1 | 235.0±36.7 | 1 645.0 | 25.0 | 1 072.4 |
| 16 | F | 757 | 7 110.8 | 1 614.2 | 1 315.6 | 6.92 | 14.5±0.5 | 72.3±7.6 | 506.1 | 23.7 | 20.2±1.6 | 207.0±39.4 | 1 449.0 | 25.1 | 942.9 |
| 807 | 6 347.3 | 1 440.9 | 1 174.3 | 6.08 | 14.9 | 75.7 | 529.7 | 22.9 | 20.7 | 223.4 | 1 564.3 | 25.0 | 1 034.6 | |
1 Total fish days = ∑(No. fish each day)
where n = 7 fish; d = 125 days
Table 4. Food conversion efficiency, survival and growth of seabass during the 125-day experiment
| Diet | Feed conversion ratio1 | Normal growth rate (g/fish/day) | P5 | Relative growth rate2 (% per day) | P5 | Protein efficiency ratio3 | P5 | Survival (%) | Apparent protein retention4 (%) | P5 | |
|---|---|---|---|---|---|---|---|---|---|---|---|
| as-fed | dry basis | ||||||||||
| A | 1.30 | 1.21 | 0.97 | a | 0.76 | a | 1.91 | a | 100 | 38.3 | a |
| A | 1.38 | 1.29 | 0.78 | 0.66 | 1.79 | 100 | 41.6 | ||||
| A | 1.50 | 1.39 | 0.62 | 0.59 | 1.65 | 100 | 33.7 | ||||
| Mean | 1.39 | 1.30 | 0.79 | 0.67 | 1.78 | 100 | 37.9 | ||||
| B | 1.24 | 1.15 | 1.04 | a | 0.81 | ab | 1.79 | a | 100 | 36.8 | a |
| B | 1.29 | 1.20 | 0.76 | 0.71 | 1.73 | 100 | 32.6 | ||||
| B | 1.16 | 1.08 | 0.89 | 0.79 | 1.92 | 100 | 36.7 | ||||
| Mean | 1.23 | 1.14 | 0.90 | 0.77 | 1.81 | 100 | 35.4 | ||||
| C | 1.21 | 1.12 | 0.77 | a | 0.72 | ab | 1.66 | a | 100 | 30.9 | a |
| C | 1.11 | 1.02 | 0.95 | 0.76 | 1.82 | 100 | 34.8 | ||||
| C | 1.27 | 1.17 | 0.83 | 0.73 | 1.59 | 100 | 31.5 | ||||
| Mean | 1.20 | 1.10 | 0.85 | 0.74 | 1.69 | 100 | 32.4 | ||||
| D | 1.48 | 1.33 | 0.76 | a | 0.69 | a | 1.56 | a | 100 | 31.9 | a |
| D | 1.40 | 1.26 | 0.79 | 0.69 | 1.65 | 100 | 32.4 | ||||
| D | 1.31 | 1.18 | 0.84 | 0.69 | 1.76 | 100 | 36.5 | ||||
| Mean | 1.40 | 1.26 | 0.80 | 0.69 | 1.66 | 100 | 33.6 | ||||
| E | 1.61 | 1.49 | 0.72 | a | 0.75 | ab | 1.23 | b | 100 | 26.0 | b |
| E | 1.45 | 1.34 | 0.92 | 0.74 | 1.37 | 85.7 | 26.3 | ||||
| E | 1.48 | 1.37 | 0.78 | 0.79 | 1.34 | 100 | 26.1 | ||||
| Mean | 1.51 | 1.40 | 0.81 | 0.76 | 1.31 | 95.2 | 26.1 | ||||
| F (Trash fish) | 5.24 | 1.19 | 1.25 | b | 0.91 | b | 1.03 | c | 100 | 20.5 | c |
| F | 5.81 | 1.32 | 1.23 | 0.84 | 0.93 | 85.7 | 17.9 | ||||
| F | 7.54 | 1.71 | 1.08 | 0.84 | 0.72 | 85.7 | 14.3 | ||||
| Mean | 6.20 | 1.41 | 1.19 | 0.86 | 0.89 | 90.5 | 17.6 | ||||
1 Feed conversion ratio = feed intake: actual weight gained by fish
2 Relative growth rate = loge Wt2-loge Wt1/Days × 100, where Wt2 = Final weight and Wt1 = Initial weight
3 Protein efficiency ratio = Wt gained by fish/protein intake
4 Apparent protein retention = (Protein deposited in fish/protein intake) × 100
5 Calculated parameters with the same superscript under P columns indicate homogeneity, as determined by Student-Newman-Keuls' multiple range test at the 5 percent significant level. Those without P columns indicate no significant difference between treatments for single classification analysis of variance (Tests were not carried out for as-fed feed conversion ratio).
3.1.3 Protein efficiency ratio (PER)
The highest values of PER which is a measure of fish weight gain per unit dietary protein intake were 1.73–1.92 (mean 1.81), obtained for seabass fed Diet B (45 percent dietary protein).
Protein efficiency ratios obtained for seabass fed Diets A and C (40 and 50 percent dietary protein) were 1.65–1.91 (mean 1.78) and 1.59–1.82 (mean 1.69) to 1, respectively. These are not significantly different from Diet B.
Protein efficiency ratios of 0.72–1.03 (mean 0.89) are significantly lower for Diet F (trash fish) in this experimental series.
3.1.4 Apparent protein retention (protein conversion efficiency)
This measures the proportion (in percent) of protein deposited in fish over total protein intake, and calculated from feed intake (Table 3b) and whole carcass composition (Table 5) records. Apparent protein retention figures are recorded in Table 4.
Table 5. Influence of experimental diets on carcass composition
| Diet No. | Percentage | |||||
|---|---|---|---|---|---|---|
| Moisture | CP | P1 | EE | Ash | P1 | |
| A | 68.3±1.9 | 21.3±1.8 | a | 3.6±0.8 | 5.1±1.0 | ab |
| B | 68.1±2.5 | 19.5±0.9 | ab | 4.0±0.6 | 7.9±1.1 | bc |
| C | 65.6±8.6 | 19.2±0.6 | ab | 4.5±1.0 | 6.9±0.8 | abc |
| D | 68.3±1.5 | 20.2±0.6 | ab | 4.2±0.2 | 6.8±1.3 | abc |
| E | 66.5±1.4 | 19.9±1.0 | b | 5.4±0.4 | 8.1±1.7 | c |
| F (control) | 69.5±1.2 | 19.7±0.4 | ab | 5.1±0.2 | 4.8±1.0 | a |
| Initial | 71.2±0.7 | 18.0±0.2 | 2.0±0.1 | 6.6±1.5 | ||
Apparent protein retention or protein conversion efficiency of fish fed all three protein reference diets (A-C) are not significantly different, but was highest (33.7– 41.6 percent, mean 37.9 percent) in fish fed Diet A. Apparent protein retention of fish fed Diets B and C were 32.6–36.8 percent, mean 35.4 percent) and 30.9–34.8 percent, mean 32.4 percent, respectively.
Apparent protein retention of fish fed trash fish ranged from 14.3–20.5 percent (mean 17.6 percent), being significantly poorer than figures for Diets A-C.
3.1.5 Protein quality comparison
Table 2 results show that amino acid levels in Diets A-C were generally comparable and higher in trash fish. Total essential amino acids were 173, 187 and 234 g/kg dry diet for A-C and 431 g/kg for trash fish, also on dry basis.
3.1.6 Digestible energy of diets
Table 1 results show that the calculated digestible energy values of Diets A-C and F (trash fish) were comparable ranging from 3 297-3 737 kcal/kg dry diet or 132–144 mg/kcal dry diet for Diets A-C and 218 mg/kcal for trash fish, also on dry basis.
The contribution of protein to total digestible energy of the protein reference diets (A-C) was 52.7–57.4 percent, whereas, this was 87.2 percent in trash fish. The contribution of fat was 31.8–35.2 percent in the reference diets, and 12.8 percent in trash fish. Carbohydrate contribution was 10.7–12.1 percent and nil, respectively. Digestible energy in trash fish is, therefore, largely derived from protein.
3.2 Performance of practical formulated diets (D and E)
Feed performance is assessed by the same factors for optimal dietary protein requirement determination, viz. fish growth rate, FCR, PER and apparent protein retention (protein conversion efficiency) and by a comparison of protein quality and digestible energy values and source.
3.2.1 Fish growth rate
The normal growth rates in fish fed Diets D and E were 0.76–0.84 (mean 0.8) and 0.72–0.92 (mean 0.81) g/fish/day, respectively. They are not significantly different from the protein reference diet (A-C) figures but are significantly lower than growth rates recorded for control fish fed trash fish, 1.08–1.25 (mean 1.19). The mean normal growth rates in fish fed Diets D and E are 67.2 and 68.1 percent of fish fed trash fish (Tables 3a, 3b and 4).
The relative growth rates of fish fed Diets D and E were 0.69 (mean 0.69) and 0.74–0.79 (mean 0.76) percent per day. The relative growth rates of control fish were 0.84–0.91 (mean 0.86) percent per day (Table 3).
3.2.2 Feed conversion ratio (Table 4)
FCRs for Diets D and E were 1.18–1.33 (mean 1.26) and 1.34–1.49 (mean 1.4), respectively. These are not significantly different from FCRs obtained with trash fish, 1.19–1.71 (mean 1.41) or with FCRs of the protein reference diets (A-C).
3.2.3 Protein efficiency ratio (Table 4)
PER in fish fed Diets D and E were 1.56–1.76 (mean 1.66) and 1.23–1.37 (mean 1.31) to 1, respectively, while those in fish fed trash fish, 0.72–1.03 (mean 0.89) to 1. The values for Diet D (local formulation) are significantly higher than those for Diet E (imported diet), while PERs from both these diets are significantly better than trash fish from the point of view of fish weight gain to protein intake.
3.2.4 Apparent protein retention (protein conversion efficiency) (Tables 1, 4 and 5)
Apparent protein retention in fish fed Diet D is significantly higher than apparent protein retention in fish fed Diet E being 31.9–36.5 percent (mean 33.6 percent) and 26.0–26.3 percent (mean 26.1 percent), respectively. Both these sets of figures are significantly higher than those for fish fed trash fish being 14.3–20.5 percent (mean 17.6 percent).
3.2.5 Protein quality comparison
Table 2 results show that amino acid levels in Diets D and E were generally comparable except for arginine (43 mg/kg dry diet) which was 1.8 times higher than in Diet D (24 mg/kg dry diet), and an amino acid essential to fish. Total essential amino acids were 187 and 193 mg/kg dry diet for D and E and 431 mg/kg for trash fish, also on dry basis.
3.2.6 Digestible energy of diets
Table 1 results show that the calculated digestible energy values of Diets D-F were comparable, ranging from 3 522–4 160 kcal/ kg dry diet or 136 and 131 mg/kcal dry diet for Diets D and E and 218 mg/kcal for F, also on dry basis.
The contribution of protein to total digestible energy of the practical formulated diets (D and E) was 54.4 percent and 52.3 percent, respectively, whereas, this was 87.2 percent in trash fish. The contribution of fat was 34.2 percent and 38.1 percent and 12.8 percent in trash fish. Carbohydrate contribution was 11.4 percent, 9.6 percent and nil, respectively.
3.3 Other performance considerations
3.3.1 Fish survival (Table 4)
There were no mortalities in fish groups fed Diets A-D. In the three replicate groups of fish fed Diet E, two had no mortalities while survival in the third replicate was 85.7 percent. Fish fed trash fish had poorer survival. Two out of three replicates survived at 85.7 percent. Analysis of survival data, however, showed no significant difference among treatments.
3.3.2 Fish condition (Tables 3a and 3b)
Fish condition was generally similar before (treatment group mean condition factor of 22.7–24.0) and after (treatment group mean condition factor of 23.3–25.0) the experiment. Diet B and trash fish fed groups were of the best condition. However, fish in general were all very healthy and devoid of skin lesions and other external clinical signs of sickness throughout the experiment.
3.3.3 Feeding rate
Feeding data is summarized in Tables 3a and 3b. Feed intake was standardized by calculating for seven fishes over 125 days for each treatment using the method of calculation of fish days, according to the method of Cho, described in Chou, 1985. Daily feed intake was 1.14 percent (mean for all treatments) for the protein reference diets (A-C), 1.17 percent for Diet D (local practical formulation) and higher, 1.28 percent for Diet E (imported seabass feed) even though crude protein and lipid levels were higher (50 percent, 16 percent) for this feed. Feeding rate using trash fish was 6.1 percent.
3.3.4 Carcass composition (Table 5)
Initial carcass moisture, crude protein, ether extractable fat and total ash were 71.2 percent, 18.0 percent, 2.0 percent and 6.6 percent, respectively. At the end of the experiment, this ranged 65.6–69.5 percent, 19.5–21.3 percent, 3.6–5.4 percent and 4.8–8.1 percent, respectively.
There was no significant difference among treatments for carcass moisture and lipid. However, fish carcass gained more fat after the experiment, this being highest in imported Diet E (5.4 percent) and trash fish (5.1 percent). Carcass lipid was lowest with Diet A which was itself the experimental diet with the lowest protein level. Fish carcass fat for Diets B-D did not vary much (4.0, 4.5 and 4.2 percent, respectively). Carcass crude protein was not significantly different among Diets A-D and trash fish control and among Diets B-E and trash fish control. Total ash in fish carcass was significantly different between Diet E and the control. Other differences were not appreciable. Ash in carcass of fish formulated diets were generally higher (1.1–1.7 times) than that of fish fed trash fish.
4. DISCUSSION
4.1 Optimal dietary protein requirement of young seabass
Seabass studied ranged from 58.0–81.8 g initially and 146.8–235.0 g at the end of the 125-day experiment.
The optimal protein reference diets in this experiment from fish response indicators are those containing 40 and 45 percent crude protein (ether extractable fat 12 percent).
4.1.1 Fish normal growth rates are not significantly different among the pelleted dry diets (A-E), ranging from 0.79–0.90 (means of replicates), but fish growth rate is significantly higher (1.19 g/fish/day) in the control group fed trash fish. The highest growth rates among the fish groups fed protein reference diets are recorded in fish fed Diet B, and range from 0.76–1.04 g/fish/day (mean 0.90 g/fish/day). This is 75.6 percent of growth rate of seabass fed trash fish.
Trash fish is a natural feed and its better protein quality and other intrinsic factors that are conducive to fish growth may be one explanation for the elevated fish response to the diet.
4.1.2 Feed conversion ratios are not significantly different among fish groups fed protein reference Diets A-C. However, best results are obtained from fish fed Diets B and C (crude protein 45 and 50 percent), being 1.14:1 and 1.10:1, respectively. Between the two diets, it would be more economical to select the lower protein Diet B. Feed conversion ratio with Diet A is 1.30:1, showing that in this experiment, more of this feed is required to produce unit weight gain than with the other two reference diets.
4.1.3 Protein efficiency ratios are highest for Diet B (1.81:1). Protein efficiency ratios in fish fed Diets A and C, although not significantly different are lower (1.78 and 1.69:1, respectively). Since protein usually constitute the most expensive component of feed price, it is important to establish the efficiency of conversion of various protein forms to the fish being cultured. In this study, protein is derived from only fish meal. The optimal level of crude protein in a formulated feed will, therefore, depend on the protein quality of ingredients used.
4.1.4 Apparent protein retention or protein conversion efficiency is significantly lower in seabass fed trash fish, (17.6 percent) and highest in Diet A (37.9 percent), followed by Diet B (35.4 percent). This shows that protein from Diets A and B is more efficiently converted into fish protein than trash fish protein. However, PER and apparent protein retention are lowest for the control diet. The standardized protein intake estimates in Table 3a affirm that although seabass fed trash fish consumed more protein, less was actually retained in seabass than with the formulated diets. Seabass in the control actually consumed 2.8 times more protein than fish fed the reference diets.
4.1.5 Protein quality, as reflected in the amino acid levels of the diets is best in trash fish and could also explain the elevated growth rate of seabass in the control groups. It is unlikely, therefore, that the significantly lower protein conversion efficiency with trash fish is due to inadequate amino acids.
4.1.6 Digestible energy of diets is comparable, but since there is less fat and no carbohydrate in trash fish to spare protein as energy source, some of trash fish protein would be used for energy. Fat is likely to spare protein in the reference diets. More of the protein is, therefore, deposited in the fish with these diets. This could explain the significantly higher protein efficiency ratios and apparent protein retention figures with the reference diets.
4.2 Performance of practical formulated diets (D and E)
Diet D formulated by the Marine Aquaculture Section is superior to Diet E, imported freshly made from overseas.
4.2.1 Fish growth rates of 0.8 and 0.81 g/ fish/day are similar for both diets while relative growth rates are 0.69 and 0.76 percent per day are not significantly different. These figures are significantly lower than those for trash fish — fed seabass (1.19 g/ fish/day, 0.86 percent per day), possibly because of better quality of trash fish protein.
4.2.2 Feed conversion ratio for Diet D is higher (1.26:1) than for Diet E (1.4:1) although the values are not significantly different. FCR for trash fish is lower (1.41:1) indicating that the trash fish is as well as converted as the dry pelleted feeds from the point of view of feed consumption to weight gain.
4.2.3 Protein efficiency ratio with Diet D is significantly higher (1.66) than Diet E (1.31), showing that weight gain is higher for unit protein intake from Diet D. The results also show that there is no protein sparing at increased lipid level (16 percent) in the imported feed (Diet E). Protein efficiency ratio with trash fish was significantly lower (0.89:1) than both these figures. The poorer performance of trash fish shows that 2.5 times more of its protein is required to elicit the higher growth response in fish.
4.2.4 Apparent protein retention is, however, significantly higher with Diet D (33.6 percent) than Diet E (26.1 percent), showing that protein quality of Diet D is better. This could be explained by possible loss of feed freshness during importation. Locally-made feeds have the added advantage of quality and availability.
4.2.5 Protein quality, as reflected in the amino acid levels of the diets is still best in trash fish and would also explain the elevated growth rate of seabass in the control groups. It is also unlikely that the lower protein conversion efficiency with trash fish is due to inadequate amino acids.
Digestible energy of diets is comparable. Again, since most of the energy is derived from protein in trash fish, PER values with this feed are significantly lower than those obtained with the formulated diets. It is likely that protein is spared by fat and carbohydrate in these diets.
4.3 Other performance considerations
4.3.1 Fish survival is generally poorer in trash fish fed groups (90.5 percent) than in groups fed dry pelleted feed (95.2–100 percent). The use of dry pelleted feed at commercial fish farms may be encouraged for this reason.
4.3.2 Fish condition is no different with dry pelleted feed or trash fish. This implies that the dry feeds may be used during the grow-out phase without compromising on fish quality. Fish carcass composition did not show a simple relationship with diet. However, ash content of fish carcass tends to be elevated with formulated feeds, reflecting the quality of the individual ingredients used. Although not statistically significant, dietary carcass lipid level was 1.7 times higher than that of fish fed trash fish. That Diet E had a higher fat level (16 percent) than the other formulations (12 percent) may explain this observation. This, however, requires confirmation especially in experiments that determine the protein-sparing effect of dietary lipid.
4.3.3 Feeding records of fish indicate that when wastage was kept to a minimum during feeding of seabass with trash fish, feeding rate was around 6 percent. The recommended rate to farmers is 8 percent (PPD, 1986) for fish of this size range. The additional 2 percent probably accounts for wastage under floating netcage conditions. In the case of dry pelleted feeds, feeding rate is around 1.1–1.3 percent under controlled conditions. Under field conditions, this should be around 1.5–2 percent, and would still be cost compatible if practical formulated feeds cost S$1.50-S$2/kg, trash fish cost being currently S$0.5/kg (as-fed).
ACKNOWLEDGMENTS
The authors wish to thank Messrs. Wong J.S. and Chua C.S. of the Nutrition Unit, Marine Aquaculture Section and the staff of the Animal Nutrition Unit, Veterinary Research and Training Institute, for their assistance in this work.
LITERATURE CITED
Adron, J.W., A. Blair, C.B. Cowey and A.M. Shanks. 1976 Effects of dietary energy level and dietary energy source on growth, feed conversion and body composition of turbot (Scopthalmus maximus L.). Aquaculture, 7:125–132.
Alliot, E., A. Febvre, A. Metailler and A. Pastoureaud. 1974 Be soins nutritifs du bar (Dicentrarchus labrax): Etude du taux de proteine et du taux de lipide dans le regime. Colloq. Aquaculture, Actes Colloq. No. 1., CNEXO edition. pp. 215–231.
Cowey, C.B., J.A. Pope, J.W. Adron and A. Blair. 1971 Studies on the nutrition of marine flatfish. Growth of the plaice Pleuronectes platessa on diets containing proteins derived from plants and other sources. Mar. Biol., 10:145–153.
DeLong, D.C., J.E. Halver and E.T. Mertz. 1958 Nutrition of salmonoid fishes. VI. Protein requirements of chinook salmon at two water temperatures. J.Nutr., 65:589–599.
Halver, J.E. 1976 Formulating practical diets for fish. J. Fish. Res. Board Can., 33:1032–1039.
Metailler, R. and C. Mery. 1977 Influence de divers aliments composes sur la croissance et la survie d'alevins de bars (Dicentrarchus labrax). Cons. Int. Explor. Mer. 3 Reunion du Groupe de Travail sur la Mariculture, Acetes Colloq. No 4, CNEXO edition. pp. 93–109.
Primary Production Department. 1986 Manual on floating netcage fish farming in Singapore's coastal waters. PP Pamphlet No. 39.
Teng, S.K., T.E. Chua and P.E. Lim. 1978 Preliminary observations on the dietary protein requirement of estuary grouper, Epinephelus salmoides Maxwell, cultured in floating netcages. Aquaculture, 15:257–271.
Yone, Y. 1976 Nutritional studies of red sea bream. Pages 39–64 in Proceedings of the First International Conference on Aquaculture Nutrition. K.S. Price, W.N. Shaw and K.S. Danberg, (eds). Lewes/Rehoboth: University of Delaware.
by
Thanom Pimoljinda1
ABSTRACT
This study was conducted to determine the effect of mixed 45 percent, 50 percent and 55 percent protein artificial diets with minced fish flesh and pure minced fish flesh diet on growth, feed conversion and survival of grouper.
Fishes with initial size of 0.91 g in weight and 4.38 cm in length were fed on the experimental diets in the 85 × 135 × 100 cm concrete tanks for 60 days.
The result revealed that the growth rate of fish fed with artificial diets plus minced fish flesh is significantly higher than the minced fish flesh alone. Survival rate of fish fed with 45 percent, 50 percent and 55 percent protein artificial diets plus minced fish flesh were 82.08 percent, 87.50 percent, 87.08 percent and minced fish flesh alone was 84.58 percent; feed conversion rates were 2.83, 2.77, 2.68 and 3.95, respectively.
1. INTRODUCTION
The brown spotted grouper (Epinephelus tauvina Forskal) is a well-known and popular fish for consumption. The fish can be cultured in ponds or cages; it is fast growing and reaches marketable size of 400–900 g in about 6–7 months. The Department of Fisheries succeeded in artificial breeding of grouper by hormone injection in 1981 at the Phuket Brackishwater Fisheries Station, 1986. Other methods of breeding include natural method and artificial technique by the dry method. Culture practice is as follows: the fry is reared in a netcage until it reaches 5–8 cm and fed with chopped fish. After attaining sufficient size the fingerlings are transferred to a netcage of 5 × 5 × 2 m at 1 000 pieces per cage. The fish is fed trash fish until attaining a weight of 400–500 g. The culture period is usually 6–7 months and food conversion ratio is 5–6:1. Production is 300–400 kg per cage. The cage culture of grouper is found throughout southern Thailand. There are about 600 cages in the coastal zone and total value of production exceeds 18–20 million baht/year. Shortage of seed remains a constraint to the expansion of grouper production.
2. MATERIALS AND METHOD
Feeding trial was conducted in twelve 1-ton concrete tanks at Phuket Brackishwater Fisheries Station. Each tank was randomly stocked with 80 grouper fingerlings with average initial weight of 0.9 g and average initial length of 4.0 cm. The duration of feeding trial was 60 days. The tank was equipped with air supply; PVC pipes and tires as shelter were provided in the tanks and water is partially changed everyday. Water quality was determined before after complete changing of water once a week.
Artificial diets were formulated to contain 45 percent, 50 percent and 55 percent protein by adjusting the fish meal and ricebran level (National Academy of Sciences, 1977) (Tables 1 and 2). The artificial diets were prepared in dry hard pellet (Pution Gloria N., 1986) and were mixed with minced fish flesh at 1:1 ratio (by weight) for appetizing before feeding. The minced fish flesh diet was prepared enough for 2–3 days use by keeping them in the freezer. A complete randomized design was used to assign the treatments in each tank. Each test diet was fed to three replicate tanks. Grouper were fed twice a day at 9:00 a.m. and 3:00 p.m. to satiation. The amount of feed consumed were recorded for determining feed conversion ratio.
1 Senior Fishery Biologist, Brackishwater Fisheries Station, Phuket, Thailand 83000
Table 1. Ingredient cost and composition of experimental diets
| Ingredients | Cost baht/kg | % | % Protein in artificial diets | Minced fish | |||||
|---|---|---|---|---|---|---|---|---|---|
| 45% baht/kg | % | 50% bhat/kg | % | 55% bhat/kg | |||||
| Fish meal | 15 | 65 | 9.1 | 75 | 10.5 | 85 | 11.0 | - | - |
| Ricebran | 5 | 33.7 | 1.75 | 23.7 | 1.25 | 13.7 | 0.75 | - | - |
| Yeast | 80/450 gms | 0.1 | 0.18 | 0.1 | 0.18 | 0.1 | 0.18 | - | - |
| Vegetable oil | 75/945 cc | 0.5 | 0.38 | 0.5 | 0.38 | 0.5 | 0.38 | - | - |
| Vitamin and mineral mixed | 28/1 pound | 0.2 | 0.123 | 0.2 | 0.123 | 0.2 | 0.123 | - | - |
| Baffin | 45 | 0.5 | 0.225 | 0.5 | 0.225 | 0.5 | 0.225 | - | - |
| Minced fish flesh | 14 | - | - | - | - | - | - | 100 | 14 |
| Total | 100 | 11.75 | 100 | 12.65 | 100 | 13.55 | 100 | 14 | |
Fifty percent of the fish stocked in each replicate was sampled at random every 15 days for growth rate study. Average total length and average body weight were measured. Measurements for total final weight and total final length of the fish from each replication were done. Net production was calculated as the difference between the total final weight and the total initial weight.
Table 2. Composition of vitamin and mineral mix used in artificial diets
| Vitamin | Units/kg of vitamins |
|---|---|
| Vitamin A | 2 000 000 units |
| Vitamin D3 | 320 000 units |
| Vitamin E | 2 000 mg |
| Vitamin K3 | 330 mg |
| Vitamin B1 | 220 mg |
| Vitamin B2 | 450 mg |
| Vitamin B12 | 4.5 mg |
| Niacin | 600 mg |
| Copper | 100 mg |
| Iron | 10 000 mg |
| Iodine | 150 mg |
| Manganese | 8 800 mg |
| Zinc | 8 000 mg |
| Cobalt | 130 mg |
| Calcium | 52 800 mg |
| Zinc Bacitacin | 4 000 mg |
3. RESULTS AND DISCUSSION
The effects of various protein levels of artificial diets mixed with minced fish flesh and minced fish flesh alone on growth rate, specific growth, feed conversion rate and survival rate in brown spotted grouper. (Epinephelus tauvina Forskal) are summarized in Table 3 and Figures 1 and 2. The average growth rates of fish fed 45 percent, 50 percent, 55 percent protein mixed with minced fish flesh and minced fish flesh alone were 0.085, 0.090, 0.085 and 0.063 cm/day or 0.252, 0.262, 0.237 and 0.167 g/day, respectively. The results of analysis of variance and Duncan's New Multiple Range Test of average growth rate of fishes (in length) showed no significance between the various protein levels of artificial diets but these were highly significant with minced fish flesh alone in which the growth rate was lowest.
Survival rate of fishes fed with the 45 percent, 50 percent, 55 percent protein level artificial diets mixed minced fish flesh were 82.08 percent, 87.50 percent, 87.08 percent and minced fish flesh alone was 84.58 percent, feed conversion rates were 2.832, 2.769, 2.683 and 3.954, respectively.
These results showed that minced fish flesh (without bone) was not sufficient as fish feed alone because of vitamins and minerals deficiency. It was found that groupers did not take the hard pellets as their food unless the pellets were mixed with minced fish flesh. From the results of this study, it showed that by using minced fish flesh alone as a diet for grouper produced low growth rate in comparison with the groupers fed with artificial diet mixed with minced fish flesh.
During the experiment water temperature observed was 26.6–31.2°C salinity ranged from 30.0–34.0 ppt and pH from 7.0–8.0.
4. CONCLUSIONS
It was found that net production and growth rate of the brown spotted groupers (Epinephelus tauvina Forskal) nursed by using artificial diets of 45 percent, 50 percent and 55 percent protein levels mixed with minced fish flesh 1:1 are higher than those by using minced fish flesh only with the food conversion rate 2.68–2.83:1 (with artificial diet) and 3.954:1 (with minced fish flesh alone, respectively). It was also proved that only hard and sink pellets are not appetizing for them.
Table 3. Results of feeding experiment in brown spotted grouper
| Diet Number | Number of fish | Average body weight (in g) | Ave. body weight (in cm) | Specific growth (g/day) | Feed conversion rate | Survival rate | ||
|---|---|---|---|---|---|---|---|---|
| Initial | Final | Initial | Final | |||||
| Artificial 45% protein + minced fish flesh | 80 | 0.940 | 16.047 | 4.435 | 9.553 | 0.252 | 2.832 | 82.08 |
| Artificial diet 50% protein + minced fish flesh | 80 | 0.887 | 16.637 | 4.438 | 9.890 | 0.262 | 2.769 | 87.50 |
| Artificial diet 55% protein + minced fish flesh | 80 | 0.854 | 15.067 | 4.322 | 9.417 | 0.237 | 2.683 | 87.08 |
| Minced fish flesh | 80 | 0.953 | 10.967 | 4.333 | 8.133 | 0.167 | 3.954 | 84.58 |
Figure 1. Average total length (cm) of (Epinephelus tauvina Forskal) grown in 60 days
5. LITERATURE CITED
National Academy of Sciences. 1977 Nutrient requirements of warm water fishes. The National Research Council, Washington, D.C. 78p.
Phuket Brackishwater Fisheries Station. 1986 The experimental on the breeding and nursing of brown spotted grouper (Epinephelus tauvina Forskal). Brackishwater Fisheries Division, Department of Fisheries. 21p.
Pution, G.N. 1986 Feed formulation and feeding. Hatchery of marine finfishes. Aquaculture Department (SEAFDEC) Philippines, Training and Extension Division. 17p.
Figure 2. Average total weight (gms) of (Epinephelus tauvina Forskal) grown in 60 days
by
Tida Pechmanee, Mavit Assavaaree1,
Paiboon Bunliptanon and Paitoon Akkayanon
1. INTRODUCTION
The grouper, Epinephelus malabaricus, is one of the commercially important fish in Thailand. In 1981, the first artificial breeding of grouper was successfully undertaken. At present, broodstocks can spawn naturally in concrete tanks. However, the survival rate of the early stage of grouper is low. The most important factor which affects the survival rate of larvae is food.
In this experiment, the result showed that it is possible to use rotifer as food for feeding 3–10 day larvae (Tables 1 and 2).
2. METHODS
2.1 Unselected rotifers were fed to 3–10 day grouper larvae; then the width of lorica rotifer found in the digestive tracts of the larvae were examined.
2.2 Two batches of grouper larvae were geared. The larvae 3–5 days were fed with less than 120 microns rotifer, the same size as found in step 1, then used all sizes of rotifer for feeding 6–20 day larvae, Artemia nauplii were fed to larvae after the 15th day of larvae growth.
2.3 Rotifers cultured with cod liver-enriched diet were then fed to the 6–20 day larvae, meanwhile, enriched Artemia nauplii were fed to larvae after the 24th day (Tables 3 and 4).
Table 1. Sizes of rotifer (lorica width) ingested by grouper larvae (ages 3–10 day) and mouth sizes of grouper larvae
| Age (day) | Length (mm) | Mouth height (microns) | Size of rotifer | Average | |
|---|---|---|---|---|---|
| Minimum | Maximum | ||||
| 3 | 2.4 | 178 | 90 | 140 | 121 |
| 4 | 2.5 | 187 | 93 | 135 | 113 |
| 5 | 2.5 | 190 | 93 | 147 | 122 |
| 6 | 2.8 | 327 | 106 | 160 | 138 |
| 7 | 3.0 | 361 | 80 | 160 | 132 |
| 8 | 3.1 | 385 | 80 | 160 | 130 |
| 9 | 3.3 | 406 | 107 | 160 | 140 |
| 10 | 4.1 | 634 | 66 | 160 | 125 |
Table 2. Distribution of lorica width of rotifers found in the
digestive track of 3–10 day old grouper larvae
(size of rotifer is mid-point of each 10 microns interval)
| Age (day) | Percentage size of rotifers in each size range (micron) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 65 | 75 | 85 | 95 | 105 | 115 | 125 | 135 | 145 | 155 | |
| 3 | 0 | 0 | 6 | 0 | 28 | 17 | 22 | 28 | 0 | 0 |
| 4 | 0 | 0 | 0 | 16 | 37 | 26 | 0 | 21 | 0 | 0 |
| 5 | 0 | 0 | 0 | 4 | 15 | 35 | 19 | 23 | 4 | 0 |
| 6 | 0 | 0 | 0 | 0 | 6 | 11 | 6 | 39 | 14 | 15 |
| 7 | 0 | 4 | 0 | 0 | 18 | 7 | 4 | 36 | 18 | 14 |
| 8 | 0 | 4 | 0 | 0 | 14 | 11 | 11 | 43 | 7 | 11 |
| 9 | 0 | 0 | 0 | 0 | 3 | 10 | 0 | 37 | 37 | 13 |
| 10 | 6 | 3 | 0 | 6 | 9 | 12 | 3 | 27 | 30 | 3 |
Table 3. Sizes of rotifer (lorica width)
| Kinds of food | Age of rotifer (hours) | ||||
|---|---|---|---|---|---|
| 0 | 6 | 12 | 24 | 48 | |
| Chlorella sp. | 92 ± 11 | 112 ± 11 | 122 ± 18 | 131 ± 9 | 139 ± 15 |
| Tetraselmis sp. | 92 ± 11 | 120 ±3 | 137±12 | 158±14 | 162±11 |
2.4 Size composition of rotifer reared in 26-ton culture tank was determined.
| Age | Crop I (68 pcs/l) |
|---|---|
| 0 (Newly hatched) | 500 l polycarbonate tank |
| 1–2 | 250 l stock seawater |
| 3–5 | Add 50 l Chlorella sp. + rotifer < 120 microns (density 5–15 idv/ml) |
| 4–6 | Add 50 l Chlorella sp. everyday |
| 7 | Transfer larvae into 1 000 l polycarbonate tank and give all sizes of rotifer after 6-day old |
| 7–15 | 50–80 percent water change |
Table 4. Sizes of rotifer feed with different foods
| Width | Length | |
|---|---|---|
| Tetraselmis sp. | 145±10 | 185±12 |
| Chlorella sp. | 137±9 | 117±11 |
| Marine yeast | 118±10 | 149±12 |
3. RESULTS AND DISCUSSION
The average size of rotifer ranged from 120 microns to 135 microns were found in the digestive tracts of the larvae of which 24 percent consisted of the 135 microns size. The biggest size of rotifers was found in the 6-day old larvae. The size distribution of the rotifer was 60 percent smaller than 120 microns and 80 percent smaller than 135 microns (Table 5), the average density of the rotifer in culture tank was 60 individual/ml. Harvesting of the rotifer was done everyday. Hence, sizes of rotifers produced were available for the 3–20 day grouper larvae requirement. From this experiment, 33–55 percent survival rate of 15-day old grouper larvae with 5.5 mm average total length was obtained (Figure 1).
Table 5. Size distribution of rotifers fed on
Chlorella sp. in 26-tons culture tank
(size of rotifer is mid-point of each 10 microns interval)
| No. | Percentage sizes of rotifers in each size range (micron) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 55 | 65 | 75 | 85 | 95 | 105 | 115 | 125 | 135 | 145 | 155 | 165 | |
| 1 | 0 | 0.8 | 1.7 | 4.2 | 10.0 | 5.0 | 10.0 | 35.8 | 16.7 | 13.3 | 2.5 | 0 |
| 2 | 0 | 0.8 | 0.8 | 3.3 | 1.7 | 0.8 | 10.0 | 49.2 | 18.3 | 11.7 | 1.7 | 1.7 |
| 3 | 0 | 0 | 0.8 | 0.8 | 5.0 | 5.0 | 10.8 | 33.2 | 19.2 | 10.8 | 10.0 | 4.2 |
| 4 | 0 | 0 | 0.8 | 0.8 | 5.8 | 5.0 | 10.0 | 30.1 | 23.3 | 19.2 | 5.0 | 0 |
| 5 | 0.8 | 0 | 0.8 | 5.0 | 9.2 | 5.0 | 13.3 | 39.2 | 15.1 | 10.8 | 0.8 | 0 |
| Average | 0.2 | 0.3 | 1.0 | 2.8 | 6.3 | 4.2 | 10.8 | 37.5 | 18.5 | 13.2 | 4.0 | 1.2 |
Figure 1. The survival rate and average total length of two crops of grouper larvae in the experiment
REFERENCES
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